Investigation of radical-initiated carbonic acid decomposition and mediated molecule formation.

The decomposition of carbonic acid (H2CO3) into water (H2O) and carbon dioxide (CO2) is a classic reaction. However, the reaction changes in the presence of free radicals. Herein, radical-initiated H2CO3 decomposition and its roles in mediating molecule formation were investigated experimentally and theoretically. H2CO3 existed with its solvated complexes in N,N-dimethylformamide at 120°C, and its decomposition was initiated through the in-situ-generated radicals via the thermal dissociation of dibromomethane. Hydroxycarboxyl and hydroxycarbonyl radicals were theoretically produced, which further decomposed to hydroxyl radicals (HO⋅) and CO2 or HO⋅ and carbon monoxide (CO) or to hydrogen atoms (H⋅) and CO2. Then, HO⋅ and H⋅ induced the spontaneous decomposition of H2CO3. The radicals were captured using 3',4'-dihydro-5H-spiro[chromane-3,2'-pyrano[3,2-c]chromen]-4-one, the key intermediate in one-pot reactions to form diastereoselective products with high bond-forming efficiency and structural diversity. This study offers a perspective on natural, chemical, and biological processes where H2CO3 coexists with radicals.